<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    
</body>
</html>
<script>
   
   var arr='haPPiA'
  function rst() {
    
     var arr1=''
     var arr2=""
    for(let i=0;i<=arr.length-1;i++){
    if(arr[i]>='a'&& arr[i]<='z'){
       arr1= arr[i].toUpperCase()
    }else{
       arr1= arr[i].toLowerCase()
    }
    arr2 +=arr1
    }
    return arr2
  }
   var arr3= rst(arr)
   console.log(arr3);
</script>